Queries about loft (attic) insulation (Post Moved)

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Old 11-09-12, 07:20 AM
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Queries about loft (attic) insulation (Post Moved)

I currently have approx 100mm thick glass fibre insulation between the joists in my loft and then chipboard has been laid over the joists for easy access and light storage (empty boxes, suitcases and all the other junk). To be honest, it looks like the insulation was a rush job on the part of the builders when the house was constructed as there's loads of 6" voids between one length of fibreglass and another i.e. no insulation.

Current UK regs call for 270mm of fibreglass in new builds for loft insulation purposes. I would like to bring the house up to meet these regs as heating costs in the UK are going through the roof (literally) at the moment! However, I'm not prepared to lose the storage space which would be the case if I used fibreglass.

What I propose is to use 80mm rigid PIR foil faced boards cut for an interference fit between the joists (the joists are 84mm x 35mm spaced at 600mm centres). I then intend to put 3mm ply over the joist and PIR board. On top of this I would like to add another layer of 80mm PIR insulation. Finally, the chipboard will go back down. In theory, the insulation alone will exceed current building regs.

The idea behind using ply is to prevent point loading (from storage and traffic etc) from compressing the top insulation board where it sits on the joist which could potentially push down on the insulation between the rafters and crack the ceiling plasterboard.

My questions are:

1) Is it OK to completely fill the joist depth with solid insulation?

2) Do I need to worry about a condensation barrier as the PIR board is foil faced?

3) Is this the best solution given that I don't want to lose access or storage in the loft area? I realise that it's not a cheap solution!

Thanks for any help / advice.

Steve
 
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Old 11-09-12, 08:42 PM
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Welcome to the forums!

Is it OK to completely fill the joist depth with solid insulation?
Yes.

Do I need to worry about a condensation barrier as the PIR board is foil faced?
A vapor barrier is always a good idea. With foil-faced rigid insulation, you should be OK. Be sure to seal places where air can get through, such as around ceiling outlet boxes.
 
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Old 11-10-12, 01:43 AM
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Thanks very much Nashkat1 for your reply!
 
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